1. Field of the Invention
The present invention is directed to the preparation of hydrogen and carbon monoxide rich gas. In particular, the invention relates to a process and reactor for the preparation of such gas by autothermal catalytic reforming of a hydrocarbon feedstock.
2. Description of the Related Art
Hydrogen and carbon monoxide rich gases are mainly used as synthesis gas in the production of ammonia and methanol or other organic compounds.
The gases find further employment during steel production and as fuel or town gas.
Industrial preparation methods most usually comprise autothermal catalytic reforming and non-catalytic partial oxidation of hydrocarbons.
During partial oxidation a hydrocarbon feedstock is combusted together with air, oxygen, or oxygen-enriched air in a burner mounted at the top of a reaction vessel. Oxygen is, thereby, supplied in amounts, which are less than the amount required for complete combustion, and hydrogen and carbon monoxide are produced in an effluent gas mainly by flame ignition reactions:CnHm+n/2O2n CO+m/2H2  (1)CnHm+n O2n CO2+m/2H2O  (2)Both reactions are strongly exothermic for all hydrocarbons.
Partial oxidation is typically employed in the gasification of heavy oils, where the temperature in the gas raises during the combustion to 1000-1500° C., which is high enough to give a sufficient low content of unconverted hydrocarbons in the combustion effluent gas. Lighter feedstocks ranging from natural gas to naphtha fractions with a boiling point up to 200° C. are conventionally treated by autothermal catalytic reforming of the feedstock.
During this process, only a part of the hydrocarbon feedstock is oxidized with an oxygen-containing atmosphere by the above flame reactions (1,2). Residual hydrocarbons in the gas stream from the combustion are then catalytic steam reformed by the endothermic reaction:CnHm+n H2On CO+(m/2+n)H2  (3)Necessary heat for the endothermic steam reforming reaction is, thereby, provided by the exothermic flame reactions (1,2).
Somewhat lower combustion temperatures are used during autothermal catalytic reforming, which is operated at a typical temperature of about 900-1400° C. Steam is added to the feed in order to moderate the flame temperature and increase hydrocarbon conversion in the burner effluent gas.
Similar to the partial oxidation process, hydrocarbon feed mixed with steam is burnt with an oxygen containing atmosphere at the top of a reactor. Residual hydrocarbons in the combusted gas are then steam reformed in the presence of a catalyst arranged as fixed bed in a lower portion of the reactor. Heat for the endothermic steam reforming reactions is supplied by the hot effluent gas from the combustion zone in the upper reactor portion and above the catalyst bed. As the combustion gas contacts the catalyst, the temperature in the gas cools to 900-1100° C. by the steam reforming reactions in the catalyst bed.
In operating the above processes, suitable hydrocarbon feed, if necessary after preheating, is introduced into a burner mounted at the top of a reactor and burnt with oxygen containing atmosphere. In order to protect the reactor shell against the high temperatures arising during the exothermic oxidation reactions, industrial reactors are provided with a temperature resistant and insulating refractory lining on the inner wall of the reactor shell.
The lining materials must be able to withstand high temperature exposure and be suited to resistant erosion by hot gases. At present, refractory materials most commonly used in industrial reactors of the above types contain more than 90% alumina.
A general problem in the preparation of synthesis gas by the above processes is formation of soot in the combustion zone at critical process conditions, such as low steam/-carbon ratios in the feedstock to the processes.
A further problem is related to start-up of the burner for the partial oxidation of the feedstock, which requires preheating of the feedstock and the reactor to high temperatures.